This invention relates to a process for the production of .DELTA..sup.2,5(10) steroids from .DELTA..sup.1,3,5(10) steroids by electrochemical reduction.
In U.S. Pat. 3,720,694 and Fed. Rep. of Germany Pat. No. P 20 63 101.0, Horst Ropke and I disclose a process for the electrolytic reduction in liquid ammonia of 19-nor-.DELTA..sup.1,3,5(10) -steroids containing a further reducible double bond. The electrolysis is conducted in an undivided (one-piece) cell employing an alkali metal salt or an alkaline earth salt of a strong acid or an onium complex salt. This results in the reduction of nonaromatic unsaturated groups but the aromatic A-ring is not affected.
The electrochemical reduction of simple aromatics in liquid ammonia has been described previously. See, for example, U.S. Pat. Nos. 3,493,477 and 3,488,266. The electrochemical reduction of .DELTA..sup.1,3,5(10) aromatic steroids to the corresponding .DELTA..sup.2,5(10) steroids in methylamine or in other alkyl amine as the solvent is known. See German Patent No. 1,266,300. However, this process has the disadvantage that the amines utilized as the solvent must be separated from the final product after the electrolysis by distillation under reduced pressure or by precipitation with other liquids. Also, due to the low conductivity of the reaction mixture, the current consumption is very high, and a correspondingly strong evolution of heat occurs. This heat must be removed in order to conduct the process on a technical scale.
Similarly, U.S. Pat. No. 3,444,057 also discloses the electrolytic reduction of .DELTA..sup.1,3,5(10) -aromatic steroids to .DELTA..sup.2,5(10) -steroids using lithium chloride, bromide or iodide as the electrolytic salt. Although liquid ammonia is contemplated as a solvent at Col. 1, line 47, of U.S. Pat. No. 3,444,057, in all of the examples ethylenediamine is employed as a solvent and the reduction is conducted in a single compartment (undivided) cell. Had the inventor actually employed liquid ammonia, he would have found that liquid ammonia is not the equivalent of ethylenediamine in such an electrolytic process and substitution of liquid ammonia as the solvent would have rendered his process inoperable to produce the desired .DELTA..sup.2,5(10) -steroids, because in a single compartment cell, i.e., an undivided cell, using lithium chloride, bromide or iodide as electrolytic salt and liquid ammonia as solvent does not result in the reduction of the aromatic ring of an aromatic steroid.
This invention is directed to a process for the electrochemical reduction of .DELTA..sup.1,3,5(10) aromatic steroids to a .DELTA..sup.2,5(10) steroid wherein the solvent can be separated from the final product without great technical effort, wherein less current is required and accordingly the amount of heat produced is not high.